Small Sunspot, Big Flare

February 7, 2000
-- This weekend a major solar flare erupted on the northeast
limb of the Sun at 1928 UT on February 5. According to data from
the NOAA Space Environment Center, it was one of the largest
and brightest optical flares of the current solar cycle.

Right: This image of the Sun was taken
through a red "H-alpha"
filter at the Holloman Air Force Base in New Mexico. The bright
spot closest to the upper left corner is the solar flare.

The eruption was bright across the electromagnetic spectrum.
It registered the maximum rating of "B" (for brilliant)
on the 3-level
scale of optical intensity for solar flares. At X-ray wavelengths
the Earth-orbiting GOES 8 satellite also detected a bright surge
that put the flare in the most powerful X-class.
Large flares like this one can emit up to 1032 ergs
of energy. This energy is ten million times greater than the
energy released from a volcanic explosion. On the other hand,
it is less than one-tenth of the total energy emitted by the
Sun every second.

The intense radiation from a solar flare travels to Earth
in eight minutes. As a result:

The Earth's upper atmosphere becomes more ionized and expands.

Long distance radio signals can be disrupted by the resulting
change in the Earth's ionosphere.

A satellite's orbit around the Earth can be disturbed by
the enhanced drag on the satellite from the expanded atmosphere.

Satellites' electronic components can be damaged.

Solar flares become more common during sunspot maximum. The
current sunspot cycle is slated to peak in mid-2000, and remain
high for at least a year.

Parents and Educators: Please visit
Thursday's Classroom
for lesson plans and activities related to this story.

Although the Feb. 5 solar flare was big and bright, it did
not come from a particularly impressive sunspot group. Active
region 8858, the site of the flare, covers just 200 millionths
of the solar disk. However, its magnetic field is complex, exhibiting
strong gradients that make it a likely site for flare activity.
Space weather forecasters expect the region to continue developing
in the coming days. If that happens, we could be in for more
major flares.

Right The animation (left) is a
three frame sequence of H-alpha images showing the progress of
the flare over a two hour period. (Frame credits: Holloman Air
Force Base, New Mexico) The still image (right) shows sunspot
group 8858 a day later on January 6, 2000. (Credit: the Solar
and Heliospheric Observatory). The two pictures are approximately
to scale. For a full disk image of the sun on January 6, 2000,
click on the still image of the sunspot group.

Just after the solar flare, the Solar
and Heliospheric Observatory (SOHO) recorded a dramatic coronal
mass ejection (CME) traveling approximately 500 kilometers per
second away from the Sun. The ejected material did not appear
to be headed for Earth. However, if this sunspot group produces
more coronal mass ejections in the coming week, they could become
Earth-directed as the active region rotates across the Sun's
central meridian.

Left: This animation shows data
obtained by SOHO's LASCO C2 coronagraph shortly after the onset
of the February 5 solar flare. To view a more complete sequence
of this coronal mass ejection click
here. The C2 coronagraph is able to observe the Sun's corona
between 1.1 and 3 solar radii. The CME was also seen by the C3
coronagraph, which has a wider view covering 3.5 to 30 solar
radii. Click
here for that animation.

Coronal mass ejections can carry up to 10 billion tons of plasma
traveling at speeds as high as 2000 km/s. When they collide directly
with Earth they can excite geomagnetic storms, which have been
linked to satellite communication failures. In extreme cases,
such storms can induce electric currents in the Earth and oceans
that can interfere with or even damage electric power transmission
equipment. Energetic particles and radiation from solar flares
reach the Earth is just minutes. The slower-moving material from
a coronal mass ejection usually takes days to reach our planet.

For more information about space weather and current
solar activity, please see SpaceWeather.com.
Technical information about current space weather condition may
be found at the NOAA Space
Environment Center. SOHO (the Solar and Heliospheric Observatory)
is a mission of international cooperation between NASA and the
European Space Agency. It is managed by the Goddard Space Flight
Center for the NASA HQ office of Space Science.Web Links